Temperature and salinity conditions in a sub-Arctic intertidal spawning habitat for capelin

Temperature and salinity were logged every 35 min during 52 days in April and May at a well-known spawning beach for capelin (Mallotus villosus) in Balsfjord, northern Norway. Two loggers were located either on or within the gravel of the spawning ground, whereas a reference logger was deployed 1 m below the lowest astronomical tide (LAT). The temperature on the gravel ranged from -5.3 to 26.78 degrees C with an overall mean of 6.2 +/- 3.6 degrees C. The diurnal temperature fluctuations (i.e. the difference between the daily maximum and minimum temperature, Delta T) varied between 3.9 and 20.8 degrees C. Sub-zero temperatures were registered neither within the gravel nor at the reference site and the overall temperature for these loggers fluctuated considerably less than on the gravel. The salinity on the surface of the gravel fluctuated markedly (5.2-28.6 psu) and contrasted the salinities registered within the gravel (1.8-6.3 psu) and below LAT (14.0-30.0 psu). The results suggest that beach-spawned capelin eggs have evolved an array of biological adaptations to survive the unpredictable physical conditions of an intertidal habitat.